**3. Targeted and nontargeted effects**

not well known to researchers. A similar situation has already appeared in mammals and aphids. An experiment on internal 137Cs irradiation in mice did not indicate any detectable change in the litter size and sex ratio [41]; in contrast, at least some of the field data have suggested adverse effects in mammals, as discussed above. Striking morphological abnormalities of aphids reported from the polluted areas [22] were not reproduced in the process of embryogenesis and egg hatching by irradiation experiments, although a change

Precise dosimetric analysis of larvae may provide additional information that satisfies dosimetrists; however, dosimetric analysis does not play a major role in reaching the conclusions stated above if the radioactivity concentration of the diet is known to us. What is important is the fact that the same experimental system was employed in studies of the pale grass blue butterfly; the two experiments simply used different types of food, i.e., either the field-harvested contaminated leaves or the artificial diet containing 137Cs. Moreover, the results from the former experiment are fully supported by the field work. Based on the butterfly case and the mammalian case discussed above, this kind of field-laboratory paradox is likely widespread among organisms of various taxa. Indeed, a literature survey showed that the controlled laboratory effects and field effects were very different in terms of their sensitivity levels; the field cases from Chernobyl were eight times more sensitive than the laboratory-controlled external

Undoubtedly, dosimetric analysis provides a different level of insight. For example, the inferred genetic mutations that are heritable over generations in this butterfly [9] are likely caused by the high-level acute exposure immediately incurred after the accident rather than by the low-level chronic exposure [12, 44, 45]. To evaluate these effects, it is important to dosimetrically understand the absorbed doses of the butterfly at the initial time of the event. In this chapter, I will discuss several important issues associated with "low-dose" radiation exposure and field effects; additionally, I propose the importance of non-dosimetric studies in conjunction with conventional dosimetric studies. Borrowing the famous phrase from Shakespeare's *Hamlet*, researchers who engage in the biological consequences of the Fukushima nuclear accident may consider the following: "*To be or not to be* (i.e., dosimetry), *that is the question.*" However, the answer is clear: both approaches are necessary to advance this scientific field to a higher level. In other words, the final answer to this question is "*to be and not to be*." I believe that this is the only way to reveal a holistic picture of the biological impacts of the Fukushima nuclear accident, which would serve as a basis for risk assessment

Multiple biological approaches should be used to understand the real-world phenomena resulting from the Fukushima nuclear accident. Furthermore, to understand biological phenomena in general, it is customary for biologists to concentrate on a few *surrogate species* or

in developmental time was detected [42].

irradiation cases [43].

52 New Trends in Nuclear Science

and management of nuclear pollution.

**2. The pale grass blue butterfly: a versatile indicator**

The dosimetric approach often states that ionizing radiation targets DNA directly or indirectly through the ionization of water molecules (hence, they are called targeted effects) and that the degree of DNA damage is linearly reflected in the biological consequences. These statements mean that biological effects can be predicted by the effective dose. Although this approach is widely accepted and utilized for assessing the biological impacts of nuclear disasters, the approach entirely ignores other potential molecular pathways and dismisses the complexity of the biological and ecological responses to the various known and unknown materials that are released from nuclear reactors.

In contrast to the conventional targeted effects, the last two decades have experienced a surge of *nontargeted effects* of ionizing radiation [51–56]. The nontargeted effects include bystander effects, genomic instability, adaptive responses, and other modes, and these nontargeted effects are likely caused by the reactive oxygen species produced by irradiation [51–56]. In this sense, the nontarget effects may be referred to as the indirect effects (note that in this chapter, nontargeted effects are classified into the same category as the direct effects as a matter of convenience to some extent). In terms of the nontargeted effects, it is important to remember that they are not readily predictable by doses, and many of them are latent. Therefore, the nontarget effects may not be detected in acute irradiation experiments, but they may manifest in the field. Furthermore, the field-laboratory paradox discussed above may have originated, at least partly, from the influence of the nontargeted effects in the field. In fact, the nontargeted effects, such as genomic instability, may have played significant roles in the observed increase in butterfly morphological abnormalities in the fall of 2012 [9, 13].

However, even the nontarget effects may not adequately explain the all effects that manifest in the field. For example, there could be possible nonradioactive by-products released from a reactor and naturally occurring nonradioactive materials that are "activated" by the radioactive materials released from a reactor. There may also be ecological interactions that could amplify small irradiation effects to larger levels throughout a food web. These possibilities may be potential sources of the *field effects* (or more precisely, *field-specific effects*), which would not be observed in controlled laboratory experiments that use an artificial source of radiation, such as 60Co and chemically pure 137Cs. However, these field-specific effects should not be confused with (or dismissed as) confounding factors because these field effects are elicited by the nuclear accident. Similarly, nontargeted effects do not have to be field-specific effects; nontargeted effects may be observed in controlled laboratory experiments that use an artificial radiation source and a simple biological system, such as a cell culture system. In other words, the nontargeted effects may be uncovered with conventional radiation biology, which investigates universal mechanisms of radiation effects, but the field-specific effects may be uncovered with *pollution biology*, which investigates the real-world phenomena; however, these two fields cannot be separated in a meaningful way in the case of nuclear accidents.

In this chapter, I refer to both the conventional targeted effects and the nontargeted effects as the "direct" effects (or "primary" effects) (**Figure 1**); however, in some literature, the nontargeted effects or one mode of the nontargeted effect are referred to as the indirect effects. It is understood that laboratory-based controlled irradiation experiments, irrespective of high or low doses, primarily examine the direct effects of ionizing radiation. In contrast, as mentioned above, other potential unconventional indirect effects of nuclear pollution are collectively called the field effects (**Figure 1**) [48, 57]. The field effects are often dependent on a biological (including ecological) context.

**4. Field effects (1): synergistic effects**

specific effects (or simply the field effects).

logical effects (**Figure 2**).

The biological indirect effects are a collective expression of all biological effects of the nuclear accident excluding the effects of the direct radiation exposure. Because any wild biological system has diverse and complex relationships with biological and chemical species, there are numerous indirect pathways that can affect organisms. Below, the field effects are roughly categorized into three groups: synergistic effects, effects from particulate matters, and eco-

**Figure 1.** Possible effects of the explosion of the Fukushima Dai-ichi Nuclear Power Plant. (a) Overall pathways. The Fukushima Dai-ichi Nuclear Power Plant released radionuclides as well as non-radionuclides that may not be fully identified. They interact with each other, and they also interact with environmental substances. Environmental substances could be natural (biotic or abiotic) or anthropogenic. The collective outputs of these interactions manifest as biological effects. The illustration of a nuclear power plant was obtained from a free illustration site called Iconrainbow (http://icon-rainbow.com/). (b) Multifaceted radiation effects. Released substances may be radionuclides or non-radionuclides, and they may be soluble or insoluble as particulate matter. Physicochemically, ionizing radiation has direct or indirect effects on the major biological target, i.e., DNA. However, both types of effects may be considered as biological direct (or primary) effects. In contrast, there are multiple biological indirect (i.e., secondary) effects, depending on the context from which the organism in question faces. The latter is often field-specific, and thus called the field-

Understanding Low-Dose Exposure and Field Effects to Resolve the Field-Laboratory Paradox…

http://dx.doi.org/10.5772/intechopen.79870

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**Figure 1.** Possible effects of the explosion of the Fukushima Dai-ichi Nuclear Power Plant. (a) Overall pathways. The Fukushima Dai-ichi Nuclear Power Plant released radionuclides as well as non-radionuclides that may not be fully identified. They interact with each other, and they also interact with environmental substances. Environmental substances could be natural (biotic or abiotic) or anthropogenic. The collective outputs of these interactions manifest as biological effects. The illustration of a nuclear power plant was obtained from a free illustration site called Iconrainbow (http://icon-rainbow.com/). (b) Multifaceted radiation effects. Released substances may be radionuclides or non-radionuclides, and they may be soluble or insoluble as particulate matter. Physicochemically, ionizing radiation has direct or indirect effects on the major biological target, i.e., DNA. However, both types of effects may be considered as biological direct (or primary) effects. In contrast, there are multiple biological indirect (i.e., secondary) effects, depending on the context from which the organism in question faces. The latter is often field-specific, and thus called the fieldspecific effects (or simply the field effects).
